/* * * YeAH TCP * * For further details look at: * http://wil.cs.caltech.edu/pfldnet2007/paper/YeAH_TCP.pdf * */ #include <linux/mm.h> #include <linux/module.h> #include <linux/skbuff.h> #include <linux/inet_diag.h> #include <net/tcp.h> #include "tcp_vegas.h" #define TCP_YEAH_ALPHA 80 //lin number of packets queued at the bottleneck #define TCP_YEAH_GAMMA 1 //lin fraction of queue to be removed per rtt #define TCP_YEAH_DELTA 3 //log minimum fraction of cwnd to be removed on loss #define TCP_YEAH_EPSILON 1 //log maximum fraction to be removed on early decongestion #define TCP_YEAH_PHY 8 //lin maximum delta from base #define TCP_YEAH_RHO 16 //lin minumum number of consecutive rtt to consider competition on loss #define TCP_YEAH_ZETA 50 //lin minimum number of state switchs to reset reno_count #define TCP_SCALABLE_AI_CNT 100U /* YeAH variables */ struct yeah { struct vegas vegas; /* must be first */ /* YeAH */ u32 lastQ; u32 doing_reno_now; u32 reno_count; u32 fast_count; u32 pkts_acked; }; static void tcp_yeah_init(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct yeah *yeah = inet_csk_ca(sk); tcp_vegas_init(sk); yeah->doing_reno_now = 0; yeah->lastQ = 0; yeah->reno_count = 2; /* Ensure the MD arithmetic works. This is somewhat pedantic, * since I don't think we will see a cwnd this large. :) */ tp->snd_cwnd_clamp = min_t(u32, tp->snd_cwnd_clamp, 0xffffffff/128); } static void tcp_yeah_pkts_acked(struct sock *sk, u32 pkts_acked, s32 rtt_us) { const struct inet_connection_sock *icsk = inet_csk(sk); struct yeah *yeah = inet_csk_ca(sk); if (icsk->icsk_ca_state == TCP_CA_Open) yeah->pkts_acked = pkts_acked; tcp_vegas_pkts_acked(sk, pkts_acked, rtt_us); } static void tcp_yeah_cong_avoid(struct sock *sk, u32 ack, u32 in_flight) { struct tcp_sock *tp = tcp_sk(sk); struct yeah *yeah = inet_csk_ca(sk); if (!tcp_is_cwnd_limited(sk, in_flight)) return; if (tp->snd_cwnd <= tp->snd_ssthresh) tcp_slow_start(tp); else if (!yeah->doing_reno_now) { /* Scalable */ tp->snd_cwnd_cnt += yeah->pkts_acked; if (tp->snd_cwnd_cnt > min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT)){ if (tp->snd_cwnd < tp->snd_cwnd_clamp) tp->snd_cwnd++; tp->snd_cwnd_cnt = 0; } yeah->pkts_acked = 1; } else { /* Reno */ tcp_cong_avoid_ai(tp, tp->snd_cwnd); } /* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt. * * These are so named because they represent the approximate values * of snd_una and snd_nxt at the beginning of the current RTT. More * precisely, they represent the amount of data sent during the RTT. * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt, * we will calculate that (v_beg_snd_nxt - v_vegas.beg_snd_una) outstanding * bytes of data have been ACKed during the course of the RTT, giving * an "actual" rate of: * * (v_beg_snd_nxt - v_vegas.beg_snd_una) / (rtt duration) * * Unfortunately, v_vegas.beg_snd_una is not exactly equal to snd_una, * because delayed ACKs can cover more than one segment, so they * don't line up yeahly with the boundaries of RTTs. * * Another unfortunate fact of life is that delayed ACKs delay the * advance of the left edge of our send window, so that the number * of bytes we send in an RTT is often less than our cwnd will allow. * So we keep track of our cwnd separately, in v_beg_snd_cwnd. */ if (after(ack, yeah->vegas.beg_snd_nxt)) { /* We do the Vegas calculations only if we got enough RTT * samples that we can be reasonably sure that we got * at least one RTT sample that wasn't from a delayed ACK. * If we only had 2 samples total, * then that means we're getting only 1 ACK per RTT, which * means they're almost certainly delayed ACKs. * If we have 3 samples, we should be OK. */ if (yeah->vegas.cntRTT > 2) { u32 rtt, queue; u64 bw; /* We have enough RTT samples, so, using the Vegas * algorithm, we determine if we should increase or * decrease cwnd, and by how much. */ /* Pluck out the RTT we are using for the Vegas * calculations. This is the min RTT seen during the * last RTT. Taking the min filters out the effects * of delayed ACKs, at the cost of noticing congestion * a bit later. */ rtt = yeah->vegas.minRTT; /* Compute excess number of packets above bandwidth * Avoid doing full 64 bit divide. */ bw = tp->snd_cwnd; bw *= rtt - yeah->vegas.baseRTT; do_div(bw, rtt); queue = bw; if (queue > TCP_YEAH_ALPHA || rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) { if (queue > TCP_YEAH_ALPHA && tp->snd_cwnd > yeah->reno_count) { u32 reduction = min(queue / TCP_YEAH_GAMMA , tp->snd_cwnd >> TCP_YEAH_EPSILON); tp->snd_cwnd -= reduction; tp->snd_cwnd = max(tp->snd_cwnd, yeah->reno_count); tp->snd_ssthresh = tp->snd_cwnd; } if (yeah->reno_count <= 2) yeah->reno_count = max(tp->snd_cwnd>>1, 2U); else yeah->reno_count++; yeah->doing_reno_now = min(yeah->doing_reno_now + 1, 0xffffffU); } else { yeah->fast_count++; if (yeah->fast_count > TCP_YEAH_ZETA) { yeah->reno_count = 2; yeah->fast_count = 0; } yeah->doing_reno_now = 0; } yeah->lastQ = queue; } /* Save the extent of the current window so we can use this * at the end of the next RTT. */ yeah->vegas.beg_snd_una = yeah->vegas.beg_snd_nxt; yeah->vegas.beg_snd_nxt = tp->snd_nxt; yeah->vegas.beg_snd_cwnd = tp->snd_cwnd; /* Wipe the slate clean for the next RTT. */ yeah->vegas.cntRTT = 0; yeah->vegas.minRTT = 0x7fffffff; } } static u32 tcp_yeah_ssthresh(struct sock *sk) { const struct tcp_sock *tp = tcp_sk(sk); struct yeah *yeah = inet_csk_ca(sk); u32 reduction; if (yeah->doing_reno_now < TCP_YEAH_RHO) { reduction = yeah->lastQ; reduction = min( reduction, max(tp->snd_cwnd>>1, 2U) ); reduction = max( reduction, tp->snd_cwnd >> TCP_YEAH_DELTA); } else reduction = max(tp->snd_cwnd>>1, 2U); yeah->fast_count = 0; yeah->reno_count = max(yeah->reno_count>>1, 2U); return tp->snd_cwnd - reduction; } static struct tcp_congestion_ops tcp_yeah = { .flags = TCP_CONG_RTT_STAMP, .init = tcp_yeah_init, .ssthresh = tcp_yeah_ssthresh, .cong_avoid = tcp_yeah_cong_avoid, .min_cwnd = tcp_reno_min_cwnd, .set_state = tcp_vegas_state, .cwnd_event = tcp_vegas_cwnd_event, .get_info = tcp_vegas_get_info, .pkts_acked = tcp_yeah_pkts_acked, .owner = THIS_MODULE, .name = "yeah", }; static int __init tcp_yeah_register(void) { BUG_ON(sizeof(struct yeah) > ICSK_CA_PRIV_SIZE); tcp_register_congestion_control(&tcp_yeah); return 0; } static void __exit tcp_yeah_unregister(void) { tcp_unregister_congestion_control(&tcp_yeah); } module_init(tcp_yeah_register); module_exit(tcp_yeah_unregister); MODULE_AUTHOR("Angelo P. Castellani"); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("YeAH TCP");